Film/nonwoven laminates are used in a wide variety of applications, including outer covers for personal care absorbent articles, such as diapers, training pants, incontinence products, feminine hygiene products, sanitary napkins, wound dressings, bandages and the like. Film/nonwoven laminates also have been found useful in the health care area in such products as surgical drapes and gowns, clean room apparel, and sterilization wrappers, as well as in roll goods, such as tent material and covers for furniture, automobiles and other vehicles. Particularly in the field of personal care absorbent articles, an emphasis has been placed on development of low cost film/nonwoven laminates that form an effective barrier to passage of bodily exudates (liquids and other waste matter), while exhibiting good aesthetic and tactile properties, such as hand feel and drape. It is desirable for the film/nonwoven laminate to simulate woven cloth in tactile properties, while still providing a barrier to bodily exudates. For specific applications, it is also desirable for the laminate to permit the passage of water vapor or other gases (breathable) while retaining liquids.
One technique employed in attempting to achieve a satisfactory, low cost film/nonwoven laminate has been to use films of increasingly lesser gauge or thickness. Thinner films typically are lower in cost and due to the reduced gauge, often have increased softness and are quieter during use. Such lower gauge films also can be rendered breathable or microporous more easily. Such thin films can have an effective gauge or thickness of 0.6 mil or less and a basis weight of 25.0 grams per square meter (gsm) or less. Particularly, when such low gauge films are achieved by drawing or stretching, such as in the machine direction, the drawing or stretching orients the molecular structure of the polymer molecules within the film in the direction of stretching, thereby increasing the strength of the film in the machine direction. However, the same machine direction oriented film is weakened in the cross machine direction in terms of tensile strength and tear properties. In order to compensate for structural weaknesses in such unidirectionally stretched films, a support layer (or multiple support layers), such as a fibrous nonwoven web, have been laminated to the film layer to form a laminate having, among other properties, increased strength and durability.
Laminates of stretch-thinned films and nonwovens have been formed using thermal lamination techniques, in which heat and pressure, as with heated pattern rolls and ultrasonics, have been employed. Thermal lamination of films and nonwovens requires, however, that the polymeric materials used in forming the film and nonwoven be thermally compatible in order to effectively laminate the two materials. Thus, thermal lamination techniques can limit the freedom to select film and/or nonwoven polymers based upon cost, processability and/or performance criteria. In addition, even thermally compatible polymers may require a level of heat and pressure that result in the laminate being undesirably stiff and/or having poor tactile properties.
Such thermally laminated film/nonwoven laminates have in some instances, particularly when employed as an outer cover for personal care absorbent articles, exhibited insufficient strength and durability properties resulting in failures of the laminate during use of such absorbent articles. This type of failure is especially pronounced when the film/nonwoven laminate is used as an outer cover for an absorbent article where garment adhesive has been applied to the outer cover for securing the absorbent article to an undergarment while in use.
Because it is desirable for the laminate to be as flexible as possible, the lamination strength between the film and nonwoven layer is frequently minimized to improve tactile properties. It is also desirable to securely hold the absorbent article to undergarments while in use by using tacky pressure sensitive garment adhesives. This can result in the situation where the film/nonwoven lamination peel strength is less than the peel strength of the nonwoven layer with applied garment adhesive to the undergarment. Thus, when the absorbent article is removed from the wearer""s undergarment, the nonwoven layer can remain attached to the undergarment while the rest of the absorbent article is removed as the film/nonwoven material delaminates. The foregoing then results in the undesirable task for the wearer to scrape, peel, or otherwise remove the remaining stuck portions of the absorbent article from their undergarment.
Therefore, there is a need for a film/nonwoven laminate, which exhibits improved tactile properties and improved removal properties when used as an outer cover for an absorbent article. There is also a need for a breathable film/nonwoven laminate with improved tactile properties and improved removal properties when used as an outer cover for an absorbent article.
An improved film/nonwoven laminate and resulting absorbent article has been invented that allows for minimum film/nonwoven lamination peel strength, thereby improving tactile properties while still removing cleanly from undergarments when used as an outer cover. It has been found that one such improved laminate and resulting absorbent article can be made by selecting an appropriate adhesive that laminates the film layer to the nonwoven layer, and simultaneously also adheres the absorbent article to undergarments while in use. The adhesive is applied to the exterior surface of the nonwoven portion of the film/nonwoven composite and through appropriate mechanisms is migrated to the interface between the film and nonwoven layer thereby laminating the two layers together. The adhesive can be used as the sole joining method for the film layer to the nonwoven layer or can assist other joining methods such as thermal bonding.
It has also been found that another improved laminate and resulting absorbent article can be made by manufacturing a laminate having at least two different bond strengths joining the laminate""s plies together. For instance, low strength thermal bonds can be used to join a large portion of the two plies, while higher strength adhesive bonds can be used to join selected portions of the plies together. This allows for construction of a laminate having improved tactile properties and improved bond peel strength.
Thus, in one aspect the invention resides in a laminate including: a liquid-impermeable first layer having a first surface, a second layer having an interior surface adjacent the first surface and an exterior surface, at least a portion of the interior surface is joined to the first surface by an adhesive applied to the exterior surface, and the adhesive having a first bond peel strength of about 1 g/mm or greater.
In another aspect, the invention resides in a laminate including: a liquid-impermeable first layer having a first surface, a second layer having an interior surface adjacent the first surface and an exterior surface, at least a portion of the interior surface is joined to the first surface by first bonds having a first bond peel strength of about 1 g/mm or greater, and at least a portion of the interior surface is joined to the first surface by second bonds having a second bond peel strength of about 3 g/mm or less.
In another aspect, the invention resides in an absorbent article including: a topsheet, a bottomsheet, and an absorbent structure disposed between the topsheet and the bottomsheet. The bottomsheet is characterized by a liquid-impermeable first layer having a first surface, a second layer having an interior surface adjacent the first surface and an exterior surface, and at least a portion of the interior surface is joined to the first surface by an adhesive applied to the exterior surface having a first bond peel strength of about 1 g/mm or greater.
In yet another aspect, the invention resides in an absorbent article including: a topsheet, a bottomsheet, and an absorbent structure disposed between the topsheet and the bottomsheet. The bottomsheet is characterized by a liquid-impermeable first layer having a first surface, a second layer having an interior surface adjacent the first surface and an exterior surface, at least a portion of the interior surface is joined to the first surface by first bonds having a first bond peel strength of about 1 g/mm or greater, and at least a portion of the interior surface is joined to the first surface by second bonds having a second bond peel strength of about 3 g/mm or less.